Method of producing a physically developable latent photographic image



METHOD OF PRODUCING A PHYSICALLY DE- VELOPABLE LATENT PHOTOGRAPHIC IMAGE No Drawing. Application February 15, 1956 Serial No. 565,559

Claims. (Cl. 96-49) This invention relates to a method for obtaining photographic contrasts with the aid of light.

This application is a continuation-in-part of copending application Serial No. 277,276, filed March 18, 1952, and now U. S. Patent No. 2,735,773.

It is known to obtain photographic contrasts by exposing a carrier which has been sensitised with a diazosulphonate followed 'by reacting the light-decomposition product produced upon exposure with a mercurous salt to form a latent mercury image which can be intensified by physical development, this term being understood to mean a method of developing according to which, prior to development, not all the metal required for building up the contrast, is present as silver ions out of crystallised compounds already present on the same spot that is blackened afterwards by this development. During this process a phenomenon, hereinafter referred to as regression occurs in which the sensitivity of the exposed carrier decreases as the length of time between exposure and formation of the latent mercury image increases.

It is an object of the present invention to increase and to stabilise the sensitivity of light-sensitive systems containing a diazosulphonate which are reacted with a mercurous salt, the latent mercury image thus produced being subjected to physical development.

In accordance with the invention, the decrease in sensitivity of the light-exposed diazosulphonate is substantially prevented by incorporating into the light-sensitive system an anti-regression agent which suppresses the tendency of the sensitivity of the exposed diazosulphonate to decrease. The term anti-regression agent as used throughout the specification and in the claims is defined as a substance which binds one or both of the lightdecomposition products formed upon exposure and/or prevents the formation of diazosulphonic acid at the exposed portions of the system. Among the antiregression agents suitable for the invention are one or more of the following:

(a) Cations which greatly reduce the concentration of sulphite ions in water and which do not oxidize mercurous salts nor react therewith with separation of mercury and/or insoluble mercury compounds and the sulphite compounds of which are capable of reacting with mercurous ions with separation of metallic mercury, these cations being in the form of salts of the photosensitive diazosulphonic acid having these ions.

(b) Water soluble weak acids and salts thereof having an acid reaction in solution and mixtures, having an acid reaction, of salts thereof with acids and which otherwise satisfy the conditions mentioned under a. V

(c) Fast coupling azocomponents which neither oxidize mercurous salts nor react therewith with separation of mercury and/or insoluble mercury compounds.

(d) Soluble benzene and naphthalene monoand polysulphonic acids and soluble salts thereof which do not oxidize mercurous salts and do not react therewith with separation of mercury and/or insoluble mercury compounds.

gtfis atnt lee (e) Soluble salts having anions which with diazonium ions yield insufficiently soluble compounds and satisfy the conditions according to c.

(f) Mixtures of substances mentioned under a to e insofar as they do give no undesired reactions with one another.

Examples of salts according to a are: p-methoxybenzene diazosulphonic acid lead salt; methyl-1 chloro-3 benzene-diazosulphon'ic acid-4 salt; o-methoxy-benzene diazosulphonic acid cadmium salt.

Examples of suitable acids according to b are: lactic acid and citric acid. Use may be made of mixtures of their alkali salts with the free acid.

As a rule, in view of the durability of the photo-sensitive layer non-volatile acids and salts of said acids should be used.

Examples of fast coupling azo components according to c are: resorcinol; l3-naphthol; amino-1 naphthol-8 bisulphonic acid-3.6; napthol-Z sulphonic acid-6 sodium salt.

Examples of benzene and napthalene, monoor polysulphonic acids according to d are: naphthalene trisulphonic acid l,5-naphthalene-disulphonic acid and m-sulpho-benzoic acid.

Examples falling under e are: ammonium tungstate and ammonium molybdate.

In all these cases mentioned under a to f, for the purpose of avoiding fog, the pH-value of the solution with which the layer is treated prior to exposure must be less than 7 and accordingly the solution, if necessary, must therefore be admixed with free acid.

While the following explanation is advanced to explain the phenomenon of regression, it is to be understood that it forms no part of the invention. Regression is believed to be due to the nature of the variation to which the,

diazosulphonate is subjected under the action of the incident light. The resultant light-reaction product results in sulphite ions being available which are capable of releasing metallic mercury from mercurous salts. This metallic mercury forms the metal image which can be intensified by physical development. The above cited substances can act as anti-regression agents if it is assumed that light-reaction converts the diazosulphonic acid into an isomeric sulphite compound from which sulphite ions are readily split off and also assuming the reaction to be reversible so that at the end of the exposure the diazosulphonic acid is again formed.

The anti-regression agents are substances which obstruct or prevent the occurrence of this reverse reaction. This prevention or obstruction may be effected either by combination of the molecule part which contains the diazonium group, the sulphite being thus set free or not being capable of combining again to form diazosulphonic acid, or by combining with the sulphite. It may be assumed that in the dry layer to which the anti-regression agent has been added, the number of the free diazonium ions and free sulphite ions is thus reduced to an extent such that the velocity of their reaction has become substantially nil. Accordingly, there is no objection to a fixed bond of the diazo part but the bond of the sulphite must be such that the bound sulphite is still capable of reacting to form mercury with the mercurous ions which are subsequently added. Finally, as an alternative, an anti-regression agent may be added which reacts both with the diazo part and with sulphite.

Consquently, it may be assumed that for example the fast-coupling azo components mentioned under 0, such for example as resorcinol, react with the diazonium residue of the exposed diazosulphonic acid, whereby a dyestuif may be produced and whereby the released sulphite ions are prevented from again forming the diazosulphonic acid in the absence of the diazonium compound.

The same remark applies to the aromatic sulphonic 3. acids mentioned under d which combine with diazonium residues to form so-called diazoaryl sulphonates.

On the other hand it may be assumed that some antiregression agents react with sulphite and thus prevent the reverse reaction.

Among them are presumably the cations mentioned under (a) and the said weak acids and salts (b); in some cases complex-formation may also play a part since in view of the very small quantities of sulphite which are produced by exposure, the low solubility of the compounds produced cannot fully account in many cases for the anti-regression effect.

It may be noted that it has been found that tests on solutions in which the quantity of sulphite is determined by analysis are not decisive for the success of the antiregression effect in a support.

A particularly intense anti-regression effect was obtained by using, as stated under 1, a mixture of anti-regression agents from which the one combines with the diazonium group and the other reacts with sulphite, for example a mixture of a cadmium salt of a diazosulphonic acid and a fast coupling azo component, or a mixture of a diazosulphonic sodium salt, a lead salt of a weak acid and a fast coupling azo component.

The sulphite ions, which, due to the exposure, are formed from the diazosulphonate abstract mercurous ions from the equilibrium Hg -Hg+++I-Ig. This results in the formation of the metallic mercury to form contrasts which can be intensified by physical development to form the metal image. Consequently, in order that satisfactory results may be obtained the reaction of the sulphite ion with the mercurous ion should preferably not be disturbed by any of the substances mentioned under (a) to (f). This accounts for the fact that not all the substances which are capable of combining with the said sulphites' are suitable for carrying out the method according to the invention. Thus, for example, the typical sulphite binders, such as the carbonyl compounds (German specification No. 642,223) are not suitable because sulphite combined in this manner no longer reacts with mercurous ions. Likewise oxidizing and reducing substances, which give unwanted reactions with mercurous ions and sulphite ions, and in addition those substances which react excessively slowly with sulphite or diazonium ions respectively are not suitable.

It has been suggested that an azo component be added to layers containing diazosulphonate (cf. British specifications 518,129 and 518,162) in order to obtain a dyestutf image after exposure from both substances by coupling, and the use of layers containing diazosulphonate and an azo component with volatile weak acids or salts thereof, such as zinc salts, is also known from German specification 734,302 and American specification 2,217,189. Formation of a dyestufi image by coupling of the diazosulphonate and the azo component is prevented in these layers by the said volatile weak acids or their salts, the dyestutf image being then formed after heating by decomposition of the salt or volatilisation of the acid respectively and, subsequent coupling of the two components under the influence of the residual basic salt or oxide.

In addition layers are known which, for the purpose of deepening the colour of the azo dyestuff image, have added to them given metal salts, for example copper or chromium salts.

All these admixtures have a function quite different from that of the anti-regression agents disclosed hereinabove since they participate in the image formation or assist in or prevent the formation of azo dyestuffs. However, if with the present invention an azo component is used this is effected under such conditions that the dyestuff produced is not contained or else does not play any important part in the ultimate image and when using salts of the above-mentioned kind azo dyestuff is generally not 4 formed at all but the metal image is produced with far less exposure and with the use of a mercurous compound.

It is preferable that the concentration of the anti regression agent not be less than of that of the diazosulphonate employed. The extent to which the regression is balanced out also depends on the choice of the diazosulphonate and even the material constituting the support for the photo-sensitive system may be of influence on the choice of the concentration. In favourable cases the regression is substantially rejected and diazosulphonates which due to regression were quite unserviceable are rendered substantially useful by the method according to the invention.

Thus, for example, it has been found that except for the use of an anti-regression agent the photo-sensitive compound 2-chloro 4-methyl benzene diazosulphonic acid sodium-1 exhibits an abnormally low sensitivity, even in the case of very quick operation, and that by addition of, for example, ammonium tungstate, to the sensitising solution the sensitivity and the blackening obtainable becomes substantially equal to those that can be obtained with paramethoxybenzene-diazosulphonate. It is also found that the colour of the silver image thus becomes deep black.

As anti-regression agent being an azo component, compounds giving a soluble dyestutf with the exposed diazosulphonate may .be conveniently used; for the well-known negative-positive dyestuff-image processes, however, such a combination cannot be used since in this case the whole image disappears during washing. However, this is not a disadvantage in the production of images according to the invention. Moreover, due to the use of much lower quantities of light the dyestutf image is very weak and insofar as it is still present it is fully covered by the physi cally developed image.

It has been further found that it is particularly useful to use as a combination of light-sensitive compound and anti-regression agent the salts of lead, cadmium, zinc and so on of a diazosulphonic acid.

A suitable test for determining whether or not a substance will be a satisfactory anti-regression agent is as follows: two solutions of the photo-sensitive substance are prepared, one with and the other without the agent under examination being provided and soaked therewith are two foils of superficially saponified cellulose-acetate which are exposed in a substantially identical manner behind a sensitometer wedge.

At the end of 10 seconds, 15 minutes and 1 hour respectively the exposed foils are treated in a mercurous salt solution and then physically developed. It will be found that a substance which is effectively active as an antiregression agent the decrease in number of blackening, respectively, of the small steps is less.

The method according to the invention is of prime importance for recording or reproducing various images one after the other on a single piece of material, such, for example, as for microdocumentation. For this purpose, layers containing a diazosulphonate may be used.

The method according to the invention is also particularly important for the production of coloured images in accordance with Netherlands specification 153,804 because in this case reproducibility is of prime importance, particularly for the production of multi-color images.

Whereverreference is made in this specification to diazosulphonate and diazosulphonic acid they are i to be understood to mean one or more organic combinations characterized by the presence of one or more groups N SO H or the salts corresponding therewith.

Example I A superficially saponified cellulose acetate foil is sensitised with a solution of 0.12 mol. p-methoxybenzenediazosulphonic acid-Pb per liter of water and then dried.

For purpose of comparison a similar foil is sensitised with a solution of 0.12 mol. p-methoxybenzene-diazosulphonic acid-Na per liter of water and dried.

Strips of both foils are cxposed using a time-scale sensitometer at a distance of 50 cms. from a 500 w. mercury-lamp. The longest exposure'time was 45 seconds and the subsequent exposure times each time were smaller than the preceding one by a value /2. Immediately after the exposure the strips are treated with a solution of 0.02 n mercurous nitrate and physically developed for 10 minutes in a solution which contains 0.5% metol, 2% citric acid and 0.2% silver nitrate.

These exposures are repeated some times with other strips of both foils, but then between the exposure and the treatment with the solution of mercurous nitrate there is a Waiting time of 15 and 60 minutes respectively.

If the sensitivity of the strips which promptly after exposure have been treated is taken to be equal to 100 then the anti-regression action of the Pb-ion is apparent from the following table:

A foil as used in Example I is sensitised with a solution of 0.15 mol. o-methoxybenzenerdiazosulphonic acid-Cd per liter of water and dried. V V v V For purpose of comparison a similar foil is sensitised with a solution of 0.15 mol. omethoxybenzene-diazosulphonic acid-Na per liter of water and dried.

Then strips of both foils are exposed, treated and developed as described in Example I with the only difference that now the mercurous nitrate solution is'0.01 11.

If the sensitivity of the strips which promptly after exposure have been treated with the mercurousl nitrate solution is taken to be equal to 100, then the antiregression action of the Cd-ion is apparent from the following table: I

Waiting time between the exposure and the treatment with the mereurous nitrate solution (in minutes) Sensitivity of the foil sensitised with the sodium salt of methoxybenzene diazosulphonic acid Sensitivity of the foil sensitised with the cadmium salt of omethoxybenzene-diazosulphonic acid Example III 7 A superficially saponified foil of cellulose acetate is sensitised with a solution containing 0.15 mol. o-methoxybenzene-diazosulphonic acid-Cd 0.02 mol. lactic acid, and 0.08 mol. sodium lactate sodium lactate as compared with the results given in Ex-y ample II, is apparent from the next table:

Waiting time between the exposure, and the treatment with the mercurous nitrate so- Sensitivity of the foil sensitised with the cadmium salt of omethoxybenzene-di- Sensitivity of the foil sensitised with the cadmium salt of omethoxybenzenediazosulphonic acid A superficially saponified cellulose acetate foil is sensitised with a solution containing 0.15 mol. o-methoxybenzene-diazosulphonic acid-Cd and 0.10 mol. 2-naphthol-6-sulphonic acid-Na per liter of water, and' dried.

The exposure of strips of the dried foil and the further treatment of the exposed strips is effected as described in Example II. If new the sensitivity of the strip which immediately after exposure has been treated with the mercurous nitrate solution is taken to be equal to 100, then the additional anti-regression action of the azo component, as compared with the results given in Example II is apparent from the following table:

. Sensitivity of the i Sensitwity ofwthe foil sensitised Waiting timebetween the-ex il sensitised with the cadposure and the treatment with the cadmium salt of owith the mercurous nitrate mium salt of omethoxybenzene-. solution (in minutes) methoxybenzencdiazcsulphonic diazosulphonic acid and the acid azo component Example V A superficially saponified foil of cellulose acetate is sensitised in a solution containing 0.'15-'rnol. o-methoxybenzene-diazosulphonic acid-Cd and 0.10 mol. 1,S-naphthalene-disulphonic acid-Na per liter of water and dried. The exposure of strips of the dried foil and the further treatment of the exposed strips are eifect'ed as described in Example II. The results thus obtained clearly point into the direction of an additional anti-regression action of the salt of the arcmatic polysulphonic acid as is apparent from the following table:

A superficially saponified cellulose acetate foil is sensitised with a solution containing 0.2 mol. p-methoxybenzene-diazosulphonic acid-Na and 0.003 mol. citric acid per liter of water was dried. For purpose of comparison Waiting time between the exposure and the treatment with the mercurous nitrate solution (in minutes) Sensitivity of the toil sensitised with the sodium saltotp-methoxybenzene -diazosuiphonic acid Sensitivity of the foil sensitised with the sodium salt of p-methcxybenzene diazosulphonic acid and citric acid practically nil..

Example VII A superficially saponified cellulose acetate foil is sensitised with a solution containing 0.2 mol. p-methoxybenzene-diaiosulphonic acid-Na 0.2 mol. lactic acid, and

0.05 mol. sodium lactate tion immediately, 15 minutes and 60 minutes respectively after exposure was 100, 70 and 45 respectively.

Example XI A foil as used in Example I is sensitised in a solution containing 0.2 mol. p-methoxy-benzene-diazolsulphonic acid sodium and 0.2 mol m-sulpho-henzoic acid sodium per liter of water and then dried. Exposure, aftertreatment and development are ettected as'described in Example I.

If the sensitivity of the foil is taken to be 100 in the case of the aftertreatment immediately following the exposure it was 60, after a waiting time of 15 minutes between exposure and after treatment and after a waiting time of 60 minutes between exposure and aftertreatment. 1

Example XII A foil as used in Example I is sensitised with a so1ution of 52 g. chloro-2-methyl-4-benzene-diazosulphonic acid-sodium-l, and 20 g. ammonium tungstate in 1000 ccm. of water.

After-drying, exposure, after treatment and development are performed as described in Example I. The antiregression eifect of the ammonium tungstate is apparent 30 from the following table: per liter of water and dried. The pH of the sensitising solution is 3.40. The exposure and the further treatment Sensitivity of Sensitivity of of the strips of this foil takes place as described in Ex- Waittngttme between exposure and the foil without the toil with ample I. In the following table the results of the antiftermatment (in mmutes) fig g g gfif fiig regression action of the mixture of lactic acid and sodium lactate is illustrated. 0 100 100 15 so 100 e0 20 75 Waiting tune between exposure and after treatment Sensitivity (in minutes) 100 40 Example XIII g8 A superficially saponified cellulose acetate foil is sensitised with a solution containing Example VIII Example IX A foil as used in Example I is sensitised with a solution containing 0.2 mol. p-methoxybenzene-diazosulphonic acid sodium and 0.2 mol. Z-naphthol per liter of 50% ethanol in water and then dried. Subsequently, exposure, treatment and development are effected as described in Example I. After storage for 0, 15 and 60 minutes between the exposure and the treatment with the mercurous nitrate solution the sensitivity expressed in the terms of Example I was 100, 70 and respectively.

Example X A foil as used in Example I is sensitised with a solution containing 0.2 mol. p-methoxybenzene-diazosulphonic acid sodium and 0.1 mol. naphthalene trisulphonic acid per liter of Water, then dried and subsequently exposed, treated and developed as described in Example I.

The sensitivity (expressed in the terms of Example I) when the foil was treated with the memurous nitrate solu- 0.15 mol. o-methoxybenzene-diazosulphonic acid sodium 0.1 mol. cadmium lactate, and 0.1 mol. resorcinol per liter of water and dried.

The foil was exposed and aftertreated as described in. Example I. The combined anti-regression action of cadmium lactate and resorcinol is apparent from the following table:

Waiting time be- Sensitivity of a Sensitivity oi a Sensitivity oi tween exposure foil without toil with cadthe foil with and aftertreatment cadmium lactate mium lactate both cadmium (in minutes) and without but without lactate and resorcinol resorcinol resorcinol 100 100 5 practically nil... 75 100 What is claimed is:

1. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive layer containing a. salt of a photo-sensitive diazo-sulphonic acid with a metal selected from the group consisting of lead, lanthanum, thorium, uranium, cadmium, zinc, chromium (HI) copper (II) and cobalt, to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a; soluble mercurous salt in the presence of moisture to form physically intensifiable contrasts.

2. A method of producing photographic contrasts as claimed in claim 1 in which the physically intensifiable contrasts are physically developed with a developing solution capable of yielding colored contrasts.

3. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive layer containing the lead salt of p-methoxy-benzene-diazosulphonic acid, to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form physically intensifiable contrasts.

4. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive layer containing the zinc salt of 1- methyl-3-chlorobenzene -4 diazosulphonic acid, to decompose said diazosulphonate and form a stable lightdecomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form physically intensifiable contrasts.

5. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive layer containing the cadmium salt of o-methoxy-benzene-diazosulphonic acid, to decompose said diazosulphonate and form a stable light-decomposiproduct and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form physically intensifiable contrasts.

6. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive layer containing a salt of a photo-sensitive diazosulphonic acid with a metal selected from the group consisting of lead, lanthanum, thorium, uranium, cadmium, zinc, chromium (III), copper (II) and cobalt and an acid reacting mixture of a weak acid having a dissociation constant smaller than and a salt thereof, to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form physically intensifiable contrasts. I

7. A method of producing photographic contrast which comprises the steps of selectively exposing portions of a light-sensitive layer containing a salt of a photo-sensitive diazosulphonic acid with a metal selected from the group consisting of lead, lanthanum, thorium, uranium, cadmium, zinc, chromium (III), copper (II) and cobalt, and an acid reacting mixture of lactic acid 10 and sodium lactate, to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form physically intensifiable contrasts.

8. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive layer containing a salt of a photo-sensitive diazosulphonic acid with a metal selected from the group consisting of lead, lanthanum, thorium, uranium, cadmium, zinc, chromium (111)), copper (II) and cobalt, and a fast coupling azo component, to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisure to form physically intensifiable contrasts.

9. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive layer containing a salt of a photosensitive diazosulphonic acid with a metal selected from the group consisting of lead, lanthanum, thorium, uranium, cadmium, zinc, chromium (III), copper (II) and cobalt, and a fast coupling azo component selected from the group consisting of 2-napthol-6-sulphonic acid sodium salt, fi-naphthol, resorcinol and l-amino-8-naphthol-3,6- bisulphonic acid, to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form physically intensifiable contrasts.

10. A method of producing photographic contrasts which comprises the steps of selectively exposing portions of a light-sensitive layer containing a salt of a photo-sensitive diazosulphonic acid with a metal selected from the group consisting of lead, lanthanum, thorium, uranium, cadmium, zinec, chromium (III), copper (II) and cobalt, and a soluble salt of an acid selected from the group consisting of benzene and naphthalene, to decompose said diazosulphonate and form a stable light-decomposition product and subjecting said light-decomposition product to the action of a soluble mercurous salt in the presence of moisture to form physically intensifiable contrasts.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE 6F CQBREC'I'ION Patent No. 2,838,398 June 10, 1958 Cornelis Johannes Dflppel et a1,

It is herby certified that error appears in the above mzmbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant, line 1, and in the heading to the printed specification,

line 4, name of second inventor, for "Jarke Jan Houtman" read Harke Jan Houtman column 10, line 36, for "zines" read zinc Signed and sealed this 5th day of August 1958.

(SEAL) Attest:

KARL H5 AXLINE I ROBERT C. WATSON Attest ng Officer Conmissioner of Patents 

1. A METHOD OF PRODUCING PHOTOGRAPHIC CONTRASTS WHICH COMPRISES THE STEPS OF SELECTIVELY EXPOSING PORTIONS OF A LIGHT-SENSITIVE LAYER CONTAINING A SALT OF A PHOTO-SENSITIVE DIAZO-SULPHONIC ACID WITH A METAL SELECTED FROM THE GROUP CONSISTING OF LEAD, LANTHANUM, THORIUM, URANIUM, CADMIUM, ZINC, CHROMIUM (III) COPPER (II) AND COBALT, TO DECOMPOSE SAID DIAZOSULPHONATE AND FORM A STABLE LIGHT-DEOCMPOSITION PRODUCT AND SUBJECTING SAID LIGHT-COMPOSITION PRODUCT TO THE ACTION OF A SOLUBLE MERCUROUS SALT IN THE PRESENCE OF MOISTURE TO FORM PHYSICALLY INTENSIFIABLE CONTRASTS. 